Objects of the invention are to provide coating apparatus which includes structures: (1) for applying melted resinous compositions which minimizes contact with air and can eliminate a film of air carried by a high-speed web into the zone of coating application; (2) for simple and effective width control in the application of the coating to the web; for enabling any leakage at the dams to flow by gravity to a catch pan rather than to be leaked onto rolls or a web entering or leaving the coating zone; (3) for eliminating excesses of coating which need to be recirculated and filtered; (4) for delivering a supply of coating under pressure to the applicator without the possibility that any leakage sustained will damage the web; (5) which result in a fountain-forming device which is simple and easily disassembled for cleaning; (6) which can subject the coating material to vacuum degasing along the supply route; (7) which result in a fountain-forming device providing good temperature and viscosity control; and (8) which provide a fountain-forming device structured for very limited distance in time of exposure of the web to coating action within the fountain so as to prevent cooling or heating of the fountain.
Coated web manufacturers are increasingly interested in applying hot-melt coatings to paper, foils, and films instead of solvent-based coatings which require fume incineration to avoid air pollution. Prior art coater types available are extrusion slot-type coaters, reverse-roll and backing roll combination types, and roll application types with knife or sickle bar doctoring off the excess from the coated web.
Conventional coaters comprise a coating carrier roll in nip relation with a reversely rotating metering roll in combination with a bath of melted resinous composition supported over the nip of the rolls for applying hot melt coatings. Though such a coater works well, there are several disadvantages. Some resinous compositions are subject to oxidation when melted and exposed to air. In a conventional coater wherein the coating liquid is gravity fed into the nip of two rolls, the pool of melted coating material is circulated in a rolling motion by the peripheries of the rolls moving through the nip in opposite directions. Air is thus pumped by the moving web and such rolling movement into the coating material supported over the nip. Another disadvantage associated with a coating bath or pool supported over the coating-forming rolls is the difficulty of keeping the dams from leaking to some degree. The leakage, even though small, can get on the backing roll and may work downward onto the web and cause damage thereto. During shutdowns, the web must be kept running until the puddle has run out before the apparatus can be shutdown. Furthermore, the coating action cannot be promptly stopped in the case of a web break or a splice passing through the nip.